Any PHP script is built out of a series of statements. A statement
can be an assignment, a function call, a loop, a conditional
statement of even a statement that does nothing (an empty
statement). Statements usually end with a semicolon. In addition,
statements can be grouped into a statement-group by encapsulating a
group of statements with curly braces. A statement-group is a
statement by itself as well. The various statement types are
described in this chapter.

if

The if construct is one of the most important
features of many languages, PHP included. It allows for
conditional execution of code fragments. PHP features an
if structure that is similar to that of C:

if (expr)
statement

As described in the section about
expressions, expr is evaluated to its
Boolean value. If expr evaluates to TRUE,
PHP will execute statement, and if it evaluates
to FALSE - it'll ignore it. More information about what values evaluate
to FALSE can be found in the 'Converting to boolean'
section.

The following example would display a is bigger
than b if $a is bigger
than $b:

<?phpif ($a > $b) echo "a is bigger than b";?>

Often you'd want to have more than one statement to be executed
conditionally. Of course, there's no need to wrap each statement
with an if clause. Instead, you can group
several statements into a statement group. For example, this code
would display a is bigger than b
if $a is bigger than
$b, and would then assign the value of
$a into $b:

<?phpif ($a > $b) { echo "a is bigger than b";$b = $a;}?>

If statements can be nested indefinitely within other
if statements, which provides you with complete
flexibility for conditional execution of the various parts of your
program.